Change icon theme?Use a theme with less separators and with a grey less grey (whiter)?Is it necessary to keep the icon on the top left?Do we have to keep the letters underlined to indicate the shortcuts?Which font is this?

Okay, you can apply any GTK theme to LXQt this way: in LXQt appearance configuration select GTK+ as widget style (and preferably in qtconfig as well), then select any theme with lxappearance-ob. For example DarkOrangeBird: